This invention relates generally to valve trains in internal combustion engines. More particularly, this invention relates to valve actuation mechanisms using rocker arms and valve bridges to actuate intake and exhaust valves in a diesel engine.
Internal combustion engines typically have rocker arms to actuate intake and exhaust valves, which permit air to enter and exit each cylinder. Commonly there are separate rocker arms to actuate a valve or pair of valves. Push rods cause the rocker arms to rotate or pivot and thereby actuate the valves. The push rods extend through the engine to connect to a camshaft. As the camshaft rotates, the push rods move the rocker arms to open and close the valves. The camshaft is designed to open and close the valves in conjunction with the cycling of the piston in the cylinder.
Recent valve actuation mechanism designs use rocker carriers and rocker arm assemblies with rocker arms made of plate material. For example, those disclosed in patent application Ser. No. 09/768,520 filed on Jan. 24, 2001, by Martin Zielke for a Rocker Carrier, and Ser. No. 09/769,610 filed on Jan. 25, 2001 by Danesh et al. for a Rocker Arm Assembly, which are hereby incorporated by reference. These patent applications are both assigned to the assignee of the present patent application, International Truck and Engine Corporation. The recent designs though improved over earlier designs have some drawbacks.
FIG. 1 illustrates a perspective view of a partial prior art valve actuation mechanism. There is shown a valve actuation linkage mechanism 100 generally comprising a valve bridge 10, a pivot foot 20, a pivot foot fastener 30 and a rocker arm 40.
FIG. 2 shows how the partial valve actuation mechanism of FIG. 1, without the valve bridge, mounted on a rocker carrier 200 which will be mounted on a cylinder head (not shown) in an internal combustion engine. The rocker arms 40 and 240 are cooperatively mounted on the rocker carrier 200 through a corresponding rocker arm pedestal or fulcrum plate 220 and fastened to the rocker carrier 200 by hold down bolts 210. The hold down bolts 210 allow the rocker arms 40 and rocker arm fulcrum plate 220 to be pre-installed to the rocker carrier 200 thereby decreasing engine manufacturing time and costs. The rocker carrier 200 shown would be mounted on one side or bank of a V-8 type engine. The rockers arms 40 and 240 shown in FIG. 2 typically have the same configuration but differ in size. FIG. 2 shows the exhaust rocker arm 40 longer and larger than the intake rocker arm 240. However, length and size of the rocker arms 40 and 240 is determined by the location of the intake and exhaust valves in relation to the rocker arm assembly. The rocker arms could be the same or different sizes depending on a particular engine application.
Referring again to FIG. 1, the valve actuation linkage mechanism 100 could be used in an engine application having four valves per cylinder. The valve bridge 10 when actuated by the rocker arm 40 via the pivot foot 25 will act on a pair of valves, e.g., a pair of intake or exhaust valves (not shown). The rocker arm generally comprises a push rod cup 60, a pivot ball cup 70, a rocker arm aperture 80, and a pivot foot end 55 having a pivot foot cup 50. The pivot foot cup 50 accepts a pivot foot 20 secured by a pivot foot fastener 30. The pivot foot fastener 30 secures the pivot foot 20 to the pivot foot cup 50 via a set of opposing pivot foot clamps 37 which are clamp or crimped on to the exterior surface of the pivot foot cup 50.
During engine operation, a push rod (not shown) actuates the rocker arm 40 via the push rod cup 60. The rocker arm 40 will pivot via a gage or pivot ball (not shown) in the pivot ball cup 70. The pivot foot 20 will in turn actuate the valves (not shown) via the Valve Bridge 10. The pivot foot 20 contacts and acts on the valve bridge 10 to actuate valve movement (not shown) in a particular cylinder. In particular, the pivot foot bottom 25 contacts the valve bridge 10 at a top bridge contact surface area 15 to actuate valve movement. The physical makeup and positioning of the valve actuation linkage mechanism 100 is such that the of the pivot foot bottom 25 is continuously sitting on or contacting the valve bridge 10 top contact surface area 15. In this manner, rocker arm 40 movement and force is immediately translated, via the pivot foot 20, to the valve bridge 10.
As the rocker arm 40 moves and pivots during engine operation, the attached pivot foot pivot travels or cycles upward or downward in an arc motion. The pivot foot""s 25 arcing motion and simultaneous mechanical contact on the valve bridge 10 results in friction wear between the pivot foot 20 and the bridge contact area 15. In essence, the pivot foot bottom surface 25 travels on the bridge contact area 15 and exerts a force with both vertical 13 and horizontal 17 elements. As the rocker arm 40 pivots during engine operation, the pivot foot bottom surface 25 exerts both a vertical force 13 and a back and forth horizontal force 17. The mechanical action between the pivot foot 20 and the valve bridge 10 results in excessive friction wear between the pivot foot contact surface 27 and the bridge contact area 15. Additionally, the pivot foot fastener 30 encounters vertical 13 and horizontal 17 forces. This degrades and loosens the connection securing the pivot foot 20 to the rocker arm 40 pivot foot cup 50. Moreover, the physical orientation and configuration of the rocker arm 40, pivot foot 20, pivot foot fastener 30 and valve bridge 10 prevent adequate oil lubrication of these interconnected and interactive parts, adding to the friction wear drawback of this design.
Thus, existing valve actuation linkage mechanisms suffer from excessive wear between the pivot foot and valve bridge at the point of contact or contact area. Accordingly, there is a need for a valve actuation linkage mechanism that can be pre-assembled and that reduces friction wear on the valve assembly during operation.
The present invention provides a valve actuation linkage mechanism for use in an internal combustion engine that reduces friction wear on the valve assembly during engine operation and can be pre-assembled resulting in decreased manufacturing time and cost. The valve actuation linkage mechanism comprises a rocker arm having a pivot rod cup, a pivot rod, a valve bridge having a pivot rod chamber, and a pivot rod retainer. The pivot rod comprises a pivot rod head, a pivot rod neck, a pivot rod body, and a pivot rod bottom. The valve bridge comprises a middle valve bridge section having the pivot rod chamber and at least one adjacent pivot rod retainer securing bore, a bottom valve bridge section, and a lubricant dimple in the pivot rod chamber. The pivot rod retainer is comprised of a pivot rod orifice having at least one pivot rod prong and at least one securing orifice.
The following drawings and description set forth additional advantages and benefits of the invention. More advantages and benefits are obvious from the description and may be learned by practice of the invention.